TN and STN systems having a twisted structure have mainly been used in liquid crystal display elements. Many liquid crystal compounds and compositions with positive dielectric constant anisotropy, which have significant roles in these TN and STN systems, have been developed. On the other hand, for the purpose of improving the narrowness of view angle which is one of the drawbacks of the above display systems having twisted structure, the display systems such as (1) the system of vertically aligning liquid crystal molecules (VA system; Vertical Alignment system) (for example, there is Japanese Unexamined Patent Application, First Publication No. Hei 2-176625) or (2) the system of rotating liquid crystal molecules in plane horizontal to a substrate by applying voltage (IPS system; In-Plane Switching system) (for example, there is published Japanese translation No. Hei 5-505247 of PCT International Publication) are proposed. In these display systems, the liquid crystal compounds and compositions with negative dielectric anisotropy have a significant role, instead of the liquid crystal compounds and compositions with positive dielectric constant anisotropy which are referred to as indispensable compounds for the display systems having twisted structure. For example, the proposal of the liquid crystal compounds and compositions with negative dielectric constant anisotropy was made in Japanese Unexamined Patent Application, First Publication No. Hei 2-4725.
For the above purpose, the development of the liquid crystal compounds having a 1,7,8-trifluoronaphthalene-2,6-diyl group has been performed. For example, several compounds are disclosed in Japanese Unexamined Patent Application, First Publication No. 2001-31597 and German Patent Application, Publication No. 19522195.
However, the methods for producing these compounds were not necessarily efficient. In Japanese Unexamined Patent Application, First Publication No. 2001-31597, a trifluoronaphthalene derivative described below is produced as an intermediate,
wherein R represents alkyl groups.
On the other hand, in the design of a composition for a liquid crystal composition, a low-volume multiproduct is obligatory since several compounds called homologues, wherein backbones of liquid crystal compounds are the same and side chains are different, are used so as to avoid the deposition of the compounds. For an efficient production, it is preferable to increase the amount to be produced once. To this end, it is of advantage to produce the compound of a common backbone and to introduce different parts at the final stage of the production. In the case of producing two sorts of homologue described below, wherein only R is different, with the method using the intermediate,
the efficiency was deteriorated since the trifluoronaphthalene backbone should be reproduced from the beginning and many intermediates are necessary. In addition, since the production, whose yield is relatively low, is performed at the final stage of the production, the loss of the high-cost intermediate is large, thereby deteriorating the efficiency badly.
On the other hand, in German Patent Application, Publication No. 19522195, the trifluoronaphthalene derivative is produced by the following pathway,
wherein Rx represents alkyl groups.
In this method, it is necessary to prepare many intermediates for the production of the above homologue. Furthermore, since Rx cannot connect the naphthalene backbone through an oxygen atom, the liquid crystal compounds, which the invention of the present application aims at, cannot be produced.
Therefore, it is desired to develop the trifluoronaphthalene derivatives, wherein it is possible to previously form the trifluoronaphthalene backbone and to introduce the other backbone later, and an efficient method for producing trifluoronaphthalene using these intermediates.